The present invention is applicable to a dual-amplifier/sample-hold circuit used in a TFT source/driver IC.
A conventional dual-sample/hold circuit includes an analog input terminal, an analog output terminal, a pair of capacitors and a pair of amplifiers and, which are connected in parallel between the input terminal and the output terminal. The sample/hold circuit stores levels of an input signal RGB and outputs an amplified signal to a TFT display. The sample/hold circuit is called “parallel two latch sample-hold/parallel two latch buffer-amplifier” type.
In operation, an input level is sampled at the capacitors alternately, and then, the sampled level is amplified by the amplifiers. This operation is repeated to output the sampled signal (level) to the output terminal alternately. For a 280-channel of TFT driver, two hundred and eighty of sample-hold circuits are required to use.
A conventional a push-pull type amplifier includes a first supply terminal VDD to which a first level of supply voltage is provided; a second supply terminal GND to which a second level of supply voltage is provided; and a control transistor unit, which is coupled between the first and second supply terminals VDD and GND. The control transistor unit includes a PMOS transistor and a NMOS transistor. Gates of the PMOS transistor and NMOS transistor are applied with bias voltage signals independently.
Levels of the bias voltage signals can be changed to control power consumption and response speed. Generally, when a level of the bias voltage applied to the PMOS transistor is increased and a level of the bias voltage applied to the NMOS transistor is decreased, power consumption is lowered and response speed is lowered. On the other hand, when a level of the bias voltage applied to the PMOS transistor is decreased and a level of the bias voltage applied to the NMOS transistor is increased, power consumption is increased and response speed becomes faster.
According to the above-described amplifier, it is difficult to decrease power consumption at the same time to increase response speed.